Transfer system for molten bath electrolyte in multi-cell electrolytic furnaces



July 4, 1961 G. CALABRIA 2,991,240

TRANSFER SYSTEM FOR MOLTEN BATH ELECTROLYTE IN MULTI-CELL ELECTROLYTIC FURNACES Filed July 9, 1957 v 4 Sheets-Sheet 1 Fig. 2

IN VEN TOR.

Maw-a July 4, 1961 G. CALABRIA 2,991,240

TRANSFER SYSTEM FOR MOLTEN BATH ELECTROLYTE IN MULTI-CELL ELECTROLYTIC FURNACES Filed July 9, 1957 4 Sheets-Sheet 2 IN VEN TOR.

July 4, 1961 s. CALABRIA 2,991,240

TRANSFER SYSTEM FOR MOLTEN BATH ELECTROLYTE IN MULTI-CELL ELECTROLYTIC FURNACES Filed July 9, 1957 4 Sheets-Sheet 3 IN V EN TOR.

y 1961 G. CALABRIA 2,991,240

TRANSFER SYSTEM FOR MOLTEN BATH ELECTROLYTE IN MULTI-CELL ELECTROLYTIC FURNACES Filed July 9, 1957 4 Sheets-Sheet 4 IN V EN TOR.

United States Pant Italy Filed July 9, 1957, Ser. No. 670,785 Claims priority, applicationltaly July 12, 1956 2 Claims. (Cl. 204-239) This invention relates to a gravity system, designed about a multi-cell electrolytic furnace, to circulate the molten bath subjected to electrolysis within the furnace during the electrolysis. It particularly concerns an electrolytic furnace structure for electrolysis of alumina, the structure containing a plurality of individual cells linked cyclically in series, by interconnecting passageways through which the molten bath liquid rllows from one cell to another, the circulation being caused by the difference in head between the cells. In its preferred form the system operates in a thermally isolated enclosure, and, in contradistinction to current conventional practice, frozen crust formation at the top of the cells is avoided. Feeding of aluminum is effected at one or more points in the circuit, while tapping-01f of aluminum is effected individually from each cell.

This invention mainly relates to a liquid transfer apparatus which is of simple and rugged construction, and which is accessibly mounted within the upper portion of the thermally insulated cell enclosure structure. This transfer device is employedto automatically, or manually, maintain the head required to establish said circulation of molten hath liquid.

An object of the present invention is to provide an improved device or system for transferring and lifting the electrolyte or fused bath from the lower end terminal chamber to the upper terminal chamber in a neck-lace type multi-cell furnace for the production of aluminum of the type described in patent application No. 587,985, filed May 29, 1956 (Patent Number 2,952,592). This lifting serves to maintain a static head between said chambers, which are at a point of junction of the neck-lace series of cells. This head ensures bath circulation through said cells, and also closes or completes the circuit of the bath circulation, at the same time.

A further object of the present improvement is to render the lifting device, and its operation, simpler and safer. It is still a further object to facilitate better adjustment of the flow, to adapt it perfectly to the requirements of the electrolysis operation, thus improving the characteristics, particularly the constancy of operation, of neck-lace type multi-cell furnaces of the type described and claimed in said copending patent application.

It is another object of the present improvement to avoid the loss of heat caused by the alternate introduction and discharge of inert gas into and from the terminal chambers. This is unavoidable if the lifting of the fused bath is carried out by pneumatic means. Consequently, the present invention serves to improve the heat balance of the furnaces. It is a further object to complete or close the liquid electrolyte circuit without electrically short-circuiting the two terminal cells of the neck-lace type multi-cell furnace, operating with closed cycle, or recirculation, of the liquid bath.

These objects and advantages, and others which will appear in the following description, are attained by employing a mechanical device for liquid transfer, in particular a device for liquid transfer comprising a mechanical ladle constituted by a rocking, or bascule type, scoop member. The member is shaped to provide a conduit or groove, and dips at one of its ends, in one of its endof-stroke positions, into the lower level bath. It thereby retains a predetermined amount of liquid, and transfers it when that end is lifted during the subsequent oscillation. It discharges the liquid from the other end into a bath at a higher level at or before reaching its other end-ofstroke position.

In the neck-lace type multi-cell furnace as described in said patent application, the bath of alumina, dissolved in fused fluorine salts, is at a temperature of from 900 to 1000 C. It circulates in the electrolysis cells con'sti tuting the furnace through special channels, by natural gravity, from a terminal chamber having a bottom at a higher level, wherein the bath is kept at a suitable head, to another chamber, namely a terminal chamber having a lower level bottom, wherein the absolute liquid level of the bath is lower than that of the preceding chamber. The difference of heights or levels corresponds to the head absorbed by the resistance of the entire liquid circuit, which head varies in accordance with the configuration of the furnace and the viscosity of the liquid circuit, but is, at any rate, of the order of magnitude of a few decimeters.

The bath liquid moves in a duct provided above the top of each of the bipolar electrodes. As described in the said copending application, the ducts are formed in ceramic blocks seated on the top face of the electrodes. The liquid and the electric current preferably move in opposed directions.

To ensure circulation, said head should be maintained between the two chambers by lifting, from the lower level chamber to the upper level chamber, an amount of liquid equal to that circulating in the furnace. This may vary between 30 and 150cc. per second, for example,

Owing to the modest quantity of liquid to be circulated, as compared with the capacity of the terminal chambers, it is not necessary for the lifting to be carried out continuously. It is even convenient to interrupt the continuity of' the liquid stream, to cause or introduce electric insulation between the liquids contained in the two terminal chambers. The voltage drop between them may easily be the maximum voltage drop, for instance volts, of the current supplied, and required for operating the neck-lace type multi-cell furnace.

Ordinary devices for transferring liquids are not applicable. The difliculties are obvious. The conventional devices could not withstand the conditions encountered, particularly in the case of fused fluorine containing salts at about 900 to 1000 C. This has strong corrosive action on almost all utilizable materials.

The device described, by way of example, in the said patent application is fairly suitable. In that device the fused bath contained in the low level chamber is periodically compelled, by the pressure exerted by means of an inert gas introduced for this purpose into the space above the liquid, to rise in an interspace until it overflows into the adjacent higher level chamber. A non-returnballtype check valve prevents the bath liquid from flowing back from the lower level chamber into the adjacent low est cell of the furnace. However, it is evident that such valve is a weak spot of the system. It will hardly be able to provide perfect sealing, so that the periodic return flow of a certain amount of bath liquid, into the adjacent terminal cell, may disturb the regular operation of said cell, although not preventing the lifting of said liquid. Moreover, if a breakdown of the valve occurs, repair, with the furnace in operation, is not an easy thing.

The periodic introduction of a fairly considerable volume of gas, and the subsequent discharge thereof, into and from the upper portion of the lower level chamber, causes loss of heat. This makes it diflicult to prevent the forming of frozen crusts at the surface of the fused bath, which crusts hinder the oscillations of liquid level that are needed for operation of the system. On the other hand, raising the gas temperature to 900 to transferred from the latter to the adjacent high terminal chamber, will be rather variable. This is evident if one bears in mind all the factors which, even with modest variations, sensibly influence said quantity. Among such factors are gas pressure, duration of the opening of inlet and outlet valves, degree of sealing tightness of the nonreturn valve, fluidity of the bath in correspondence with or relation to the channel connecting the two chambers. Hence, adjusting the flow requires careful handling and attention.

The inconveniences mentioned are obviated by the device according to the present invention. Preferred embodiments are described with reference to the accompanying drawings, in which:

FIG. 1 is a cross section of the neck-lace type furnace taken along a plane intersecting the two terminal chambers, being a side view of the oscillating ladle for transferring the bath liquid, according to one embodiment of the invention;

, FIG. 2 is a schematic section, in larger scale, showing the pivot of the oscillating ladle of FIG. 1;

FIG. 3 is a section taken along the line A-A of FIG. 1;

multi-cell furnace in one of its most typical arrangements.

At 1 is the lower level chamber in which is collected the bath liquid coming from the adjacent last cell 2 (FIG. 3) of the neck-lace through the channels 3. At 4 (FIG. I) is the higher level chamber which feeds the adjacent first cell of the neck-lace through the channels 5. The two terminal chambers are separated by a wall 6 and closed by a cover 7. The heat insulation of the side walls 8 and of the cover 7, without taking into account that of the wall 6, is such as to ensure the keeping of the bath and gas, at top, at a temperature of for instance 950 C., and in such a way as to also ensure the fluidity of the bath in the superficial layers. The side walls 8 and the partition wall 6 are internally lined where they contact with the bath of fused salts, either with baked carbon paste, similar to that used to line the bottoms of present-day conventional cells for aluminum electrolysis, or with graphite, or with the inert and electrically insulating protective materials 9 mentioned in said copending patent application.

Resistors (not shown in the drawings), for instance of the material called silite, applied under the covers prevent the temperature from dropping below the so-called critical temperature. This is the temperature at which the viscosity of the bath liquid tends sensibly to increase. In the partition wall 6, which generally does not reach as far as the cover 7, there are provided one or more slits 10 just wide enough to permit the accommodation of a bascule rockers, described hereinafter. The lower surface 11 of slit 10 is conveniently shaped as a slide inclined and conveying towards the higher level chamber. In the slit, or slits, 10 there are accommodated one or more bascule rockers 12 made of a material that resists a 4 temperature of about 1000 C. and is not attacked by the bath liquid. Graphite may be used or metal alloys suitable for use at high temperatures, such as stainless steel of high percentage alloy with an austenitic structure of A151 310 standard type (25% chromium, 20% nickel), or a molybdenum-steel alloy such as the commercial alloy Hastelloy (60% nickel, 20% molybdenum, 18-20% iron), or a chromium-nickel-cobalt-iron alloy such as Multimet alloy (N-155). Alternately, there may be used a nickel alloy with nickel containing chromium and iron, as well as possible titanium and aluminum, such as Inconel alloy. These alloys retain good mechanical characteristics at 1000 C. temperature. Said materials are preferaply coated with a protective layer, for example of carbon electrode paste or magnesium oxide.

In order to prevent oxidation of the carbonaceous material, in the space at top of the bath in the two chambers there is maintained a reducing or neutral atmosphere, by introducing waste furnace gas, or nitrogen, in slight excess of pressure over that of the exterior atmosphere; or by depositing, on special supports (not shown in the drawings), minute size particles of charcoal which burn the oxygen that may penetrate, with outside air, through leaks in the covers or walls.

The bascule rocker comprises a hollow ladle. In the examples illustrated it is a channel member of U-shaped cross section. Any shape may be adopted provided that it ensures the necessary mechanical strength and provides a longitudinal passage-way for the liquid from one end to the other. The channel end facing the higher level chamber 4 is shaped as a pouring means and, therefore, it is fully open. The opposed end 13 is shaped as a scoop, as a bucket for example. It is open at top but at least partly closed and widened at its heading face. The bascule rocker is pivoted laterally, a preferred embodiment of pivot being illustrated in FIGS. 1, 2 and 3, where it is shown carrying, laterally, two pivots l4 preferably shaped as wedges or knives, to offer less resistance by friction, said knives resting in notches 15. The latter are conveniently shaped so that the rocker may freely oscillate on said knives. The oscillatory movement is between one end position in which the scoop end is sub merged in the liquid of chamber 1 and the rocker comes close to the partition wall 6 at sloped portion 16, and the opposed end position in which the scoop is lifted and the rocker comes close to the sliding and conveying bottom of said partition wall at sloped portion 17. Oscillatory motion is imparted to the rocker by means of any well known, simple device. The transmission of the movement may be effected in various ways, depending upon the general arrangement of the furnace. A convenient manner is that illustrated in FIGS. 1 and 3. It comprises a tappet rod 18 which descends vertically through the cover and slide seat 18 to press arm 20 against the shorter side of the rocker, thus compelling the scoop to rise. When tappet 18 is free to move upwardly it allows the scoop to go down again, under its own weight, by gravity.

The tappet 18-20 is controlled through a rotary cam 21, or through an equivalent connecting means. When the cam face assumes a certain position the tappet is free to be moved upwardly by the weight of the scoop. To make the rod 18 slide better, it may be made of metal coated with graphite. The tappet may be conveniently slightly inclined instead of being vertical, as represcntcd in the drawing for the sake of simplicity. The sealing of the passage-way 22 through the cover need not be perfect, without damage, as has been found.

Another convenient system is that illustrated in FIGS. 4, 5 and 6, as another embodiment. The bascule rocker is mounted on a central pivot member seated between flanges 27, for example, on a part 26 of quadrangle cross section, forming part of a shaft 23. The end 24 of shaft 23 projects outside the furnace and is coupled there to a suitable device that imparts a reciprocating rotary movemerit to it. This arrangement is particularly suitable if a plurality of scoops are provided. The external mechanism (not shown) for controlling the oscillations of the rocker or rockers may be any one of a great variety of types known per se. For convenience such mechanism should permit the variation of the frequency of said oscillations. The cam 21 and tappet 18 can be readily adapted to this purpose, by employing a lever attached to arm 24.

The operation of the device is self-explanatory. At every oscillation the fused bath of the lower level chamher is loaded, in a pre-determined quantity, into the scoop, which is then lifted, said quantity of bath liquid flowing along the longitudinal cavity or channel of the rocker ladle. When the latter assumes an inclination opposed to the loading position, said liquid quantity leaves the opposed end of the ladle and flows down the partition wall 11, shaped as a slide, until it reaches the liquid contained in the higher level chamber. The quantity of liquid lifted may be easily adjusted by varying the number of oscillations per hour so as to keep the higher level of the desired value. For this purpose any conventional clock-work mechanism, controlling a motor turning cam 21, can be employed. There may be provided, in the partition wall, an overflow 25 whose threshold is at the maximum height level, which the liquid should not surpass. The overflow discharges into the lower level chamber any excess that, for any reason, might occur over the flow in the furnace, for example due to the clogging of channels between one cell and the other.

The extreme simplicity of the mechanism ensures its perfect operation.

The frequency of oscillations may be kept low enough to avoid violent shocks and stresses. By way of example, if the average flow required is 100 cc. per second, it is possible, by proportioning the scoop so as to make it contain 500 cc, in minimum level height conditions of the bath liquid in the lower chamber, to employ a frequency of one oscillation every five seconds. The frequency may be diminished at will, by increasing the capacity of the scoop, or by providing two scoops.

Where it is desired to increase the quantity of liquid lifted at every oscillation, the capacity of the scoop may be increased without modifying its volume, merely by partly covering its cavity, at the end.

The pivots placed outside the bath turn through only a fraction of a complete revolution and are always stressed by a component directed downwards. This permits use of a knife-type support, as in scales, alfording minimum friction, and not requiring any lubrication or maintenance.

Projection to the outside of only one single mobile member is required, which may be provided through an aperture. This aperture has no special requirements in respect to sealing tightness, as stated above.

There are no valves or delicate members and the entire mechanism exposed to the heavy duty conditions of the environment is constituted by one single piece having no strict dimensional and adjustment requirements, so that it can operate even if worn out, or deformed to a certain extent. On the other hand, the entire mobile part can be removed and replaced by means of a very simple operation. The entire mechanism can be inspected, and is accessible, by lifting the cover of the terminal chambers, so that its servicing can be made without any difficulty during furnace operation.

Heat-insulation of the chambers and of the device can be provided easily since the only discontinuity in the external surface and the only opportunity for direct heat loss is constituted by the passage-way for the control rod, the tappet 18 and pivot member 24 respectively. This may be reduced to negligible importance. The mechanical eifort or force needed for operation is reduced to a minimum by counterweighting the shorter arm of the bascule rocker. Hence it can be stated that the instal- 6 lation and operation cost of the complete device is reduced to a fraction of that of the other devices hereto fore proposed for analogous purposes. The regularity of operation and efiiciency of the device are very satisfactory, and by means of this improvement, the problem of the lifting of the fused bath in neck-lace type multi-cell furnaces is satisfactorily solved.

Moreover, apart from neck-lace type furnaces, the

device may find advantageous uses also in all those cases in general in which it is required to lift moderate, adjustable quantities of liquids to heights of a few decimeters in the presence of corrosive media or elevated temperatures which make safe operation of more complicated devices difiicult. It should be understood also that the scope of the invention is not limited to the examples or embodiments described, but includes their structural and functional equivalents.

I claim:

1. In a high temperature furnace comprising a heatinsulated structure providing a processing chamber adapted to contain a bath of molten liquid, the combination therewith comprising two liquid circulating chambers within the insulated structure, a first one of said circulating chambers having an intake passage communicating with the processing chamber, said intake passage being at a level to receive molten bath liquid from said processing chamber by gravity flow, the second one of said circulating chambers having an outlet passage communicating with said processing chamber to return molten bath liquid thereto, said outlet passage being at a higher level than said intake passage and at a level high enough to return the molten bath liquid by gravity flow to the processing chamber, a communicating duct in said insulated structure between the two chambers for passage of molten bath liquid from the first circulating chamber to the second, the duct communicating with the two circulating chambers above the said intake and outlet passages thereof, means in said heat-insulated structure to cause said molten bath to circulate by gravity from said second chamber, through the processing chamber, and back to said first chamber, said means comprising a pivoted rocker member partly extending into said duct and having a scoop portion which in one position of the rocker dips into the liquid of the first chamber, the rocker member providing a conveying portion communicating with the scoop portion into which the liquid flows from the scoop portion when the latter is raised, the conveying portion thereupon supplying the liquid to the second chamber, and means for oscillating the rocker.

2. In a high temperature furnace comprising a heatinsulated structure providing a processing chamber adapted to contain a bath of molten liquid, the combination therewith comprising two liquid circulating chambers within the insulated structure, a first one of said circulating chambers having an intake passage communicating with the processing chamber, said intake passage being at a level to receive molten bath liquid from said processing chamber by gravity flow, the second one of said circulating chambers having an outlet passage communicating with said processing chamber to return molten bath liquid thereto, said outlet passage being at a higher level than said intake passage and at a level high enough to return the molten bath liquid by gravity flow to the processing chamber, a communicating duct in said insulated structure between the two chambers for passage of molten bath liquid from the first circulating chamber to the second, the duct communicating with the two circulating chambers above the said intake and outlet passages thereof, the bottom wall of the second circulating chamber'being at a height above that of the bottom wall of the first circulating chamber, and a liquid overflow duct connecting the two circulating chambers to limit the height of the liquid in the second circulating chambenmeans in said heat-insulated structure to cause said molten bath to circulate by gravity from said second chamber, through the processing chamber, and back to 'said first chamber,

said means comprising a pivoted rocker member partly extending into said duct and having a scoop portion which in one position of the rocker dips into the liquid of the first chamber, the rocker member providing a conveying portion communicating with the scoop portion into which the liquid flows from the scoop portion when the latter is raised, the conveying portion thereupon supplying the liquid to the second chamber, and means for oscillating the rocker.

3. In a high temperature furnace comprising a heat insulated structure providing a processing chamber adapted to contain a bath of molten liquid, the improvement comprising two liquid circulating chambers within the insulated structure, a first one of said circulating chambers having an intake passage communicating with the processing chamber, said intake passage being at a level to receive molten bath liquid from said processing chamber by'gravity flow, the second one of said circulating chambers having an outlet passage communicating with said processing chamber to return molten bath liquid thereto, said outlet passage being at a higher level than said intake passage and at a level high enough to return the molten bath liquid by gravity fiow to the processing chamber, an upwardly opening communicating duct in said insulated structure between the two chambers for passage of molten bath liquid from the first circulating chamber to the second, the duct communicating with the two circulating chambers above the said intake and outlet passages thereof, means in said heat-insulated structure to cause said molten bath to circulate by gravity from said second chamber, through the processing chamber, and back to said first chamber, said means comprising a pivoted rocker member partly extending into said duct and having a scoop portion which in one position of the rocker dips into the liquid of the first chamber, the rocker member providing a conveying portion communicating with the scoop portion into which the liquid flows from the scoop portion when the latter is raised, the conveying portion thereupon supplying the liquid to the second chamber, said insulated structure including cover means for the duct, the two chambers and the cells, and means for oscillating the rocker, said means including an operating element extending through the insulated structure, and a device outside the latter to energize said operating element.

4. In a high temperature furnace comprising a heatinsulated structure providing a processing chamber adapted to contain a bath of molten liquid, the improvement comprising two liquid circulating chambers within the insulated structure, a first one of said circulating chambers having an intake passage communicating with the processing chamber, said intake passage being at a level to receive molten bath liquid from said processing chamber by gravity flow, the second one of said circulating chambers having an outlet passage communicating with said processing chamber to return molten bath liquid thereto, said outlet passage being at a higher level than said intake passage and at a level high enough to return the molten bath liquid by gravity flow to the processing chamher, an upwardly opening communicating duct in said insulated structure between the two chambers for passage of molten bath liquid from the first circulating chamber to the second, the duct communicating with the two circulating chambers above the said intake and outlet passages thereof, means in said heat-insulated structure to cause said molten bath to circulate by gravity from said second chamber, through the processing chamber, and back to said first chamber, said means comprising a pivoted rocker member partly extending into said duct and having a scoop portion which in one position of the rocker dips into the liquid of the first chamber, the rocker member providing a conveying portion communicating with the scoop portion when the latter is raised, the conveying portion thereupon supplying the liquid to the sec- 0nd chamber, said insulated structure including cover means for the duct, the two chambers and the cells, and means for oscillating the rocker, said means including an operating element extending through the insulated structure, and a device outside the latter to energize said operating element, said duct having a bottom wall sloping downwardly toward the second circulating chamber, the conveying portion of the rocker member approaching said sloping bottom wall when the scoop portion is raised, to deliver the liquid to said wall, and a liquid overflow duct connecting the two circulating chambers to limit the height of the liquid in the second circulating chamber.

5. In an electrolysis furnace comprising a heat-insulated structure containing a plurality of electrolytic cells, the cells being adapted to contain a molten bath to be electrolyzed and having cathodes and anodes, adjacent cells having intercommunicating passages at respectively diminishing levels for serial flow, by gravity, of molten bath liquid among the cells, the improvement comprising two adjacent chambers within the insulated structure, a first one of said chambers having an intake passage conimunicating with a cell, said intake passage being at a level to receive molten bath liquid from said cell by gravity flow, the second one having an outlet passage communieating with a second cell to return molten bath liquid thereto, said outlet passage being at a higher level than said intake passage and at a level high enough to return the molten bath liquid by gravity flow to the second cell, an upwardly opening communicating duct in said insulated structure between the two chambers for passage of molten bath liquid from the first chamber to the second, the duct communicating with the two chambers above the said intake and outlet passages, means in said heat-insulated structure to cause said molten bath to circulate by gravity among the cells, from said second chamber, through the cells, and back to said first chamber, said means comprising a pivoted rocker member partly extending into said duct and having a scoop portion which in one position of the rocker dips into the liquid of the first chamber, the rocker member providing a conveying portion communicating with the scoop portion into which the liquid fiows from the scoop portion when the latter is raised, the conveying portion thereupon supplying the liquid to the second chamber, said insulated structure including cover means for the duct, the two chambers and the cells, and means for oscillating this rocker, said means including an operating element extending through the insulated structure, and a device outside the latter to energize said operating element.

6. In an electrolysis furnace comprising a heat-insulated structure containing a plurality of electrolytic cells, the cells being adapted to contain a molten bath to be electrolyzed and having cathodes and anodes, adjacent cells having intercommunicating passages at respectively diminishing levels for serial flow of molten bath liquid by gravity among the cells, the combination therewith comprising two adjacent chambers within the insulated structure, a first one of said chambers having an intake passage communicating with a cell, said intake passage being at a level to receive molten bath liquid from said cell by gravity flow, the second one having an outlet passage communicating with a second cell to return molten bath liquid thereto, said outlet passage being at a higher level than said intake passage and at a level high enough to return the molten bath liquid by gravity flow to the second cell, an upwardly opening communicating duct in said'insulated structure between the two chambers for passage of molten bath liquid from the first chamber to the second, said duct having a bottom wall sloping downwardly toward the second chamber, the duct communicating with the two chambers above the said intake and outlet passages, means in said heat-insulated structure to cause said molten bath to circulate by gravity among the cells, from said second chamber, through the cells, and back to said first chamber, said means comprising a pivoted rocker member partly extending into said duct and having a scoop portion which in one position of the rocker dips into the liquid of the first chamber, the rocker member providing a conveying portion communicating with the scoop portion when the latter is raised, the conveying portion thereupon approaching the downwardly sloping bottom portion of the duct and supplying the liquid to the second chamber, said insulated structure including cover means for the duct, the two chambers and the cells, and means for oscillating this rocker, said means including an operating element extending through the insulated structure, and a device outside the latter to energize said operating element.

7. In an electrolysis furnace comprising a heat-insulated structure containing a plurality of electrolytic cells, the cells being adapted to contain a molten bath to be electrolyzed and having cathodes and anodes, adjacent cells having intercommunicating passages a-t respectively diminishing levels for serial flow, by gravity, of molten bath liquid among the cells, the improvement comprising two adjacent chambers within the insulated structure, a first one of said chambers having an intake passage communicating with a cell, said intake passage being at a level to receive molten bath liquid from said cell by gravity flow, the second one having an outlet passage communicating with a second cell to return molten bath liquid thereto, said outlet passage being at a higher level than said intake pasage and at a level high enough to return the molten bath liquid by gravity flow to the second cell, an upwardly opening communicating duct in said insulated structure between the two chambers for passage of molten bath liquid from the first chamber to the second, the duct communicating with the two chambers above the said intake and outlet passages, the bottom wall of the second chamber being at a height above that of the bottom wall of the first chamber, and a liquid overflow duct connecting the two chambers to limit the height of the liquid in the second chamber, means in said heat-insulated structure to cause said molten bath to circulate by gravity among the cells, from said second chamber, through the cells, and back to said first chamber, said means comprising a pivoted rocker member partly extending into said duct and having a scoop porton which in one position of the rocker dips into the liquid of the first chamber, the rocker member providing a conveying portion communicating with the scoop portion into which the liquid flows from the scoop portion when the latter is raised, the conveying portion thereupon supplying the liquid to the second chamber, said insulated structure including cover means for the duct, the two chambers and the cells, and means for oscillating the rocker, said means including an operating element extending through the insulated structure, and a device outside the latter to energize said operating element.

8. The apparatus defined in claim 3, the rocker member being pivoted off-center, the operating element comprising a tappet acting upon the shorter arm of the rocker member.

9. The apparatus defined in claim 5, the rocker member having a transversely extending recess of non-circular form, and a rotary shaft having a section fitting into said recess, the duct being in a partition wall between the two chambers, the shaft being pivotally supported in the partition wall and having a portion extending through the furnace Wall, said portion comprising said operating element.

10. The apparatus defined in claim 5, the rocker and operating element being of carbonaceous material reinforced internally.

11. The apparatus defined in claim 5, the rocker and operating element being of MgO reinforced internally, the MgO being electrofused and heat treated.

12. The apparatus defined in claim 5, the rocker and operating element being made of an iron alloy resistive to high temperatures.

References Cited in the file of this patent UNITED STATES PATENTS 604,242 Vance May 17, 1898 637,851 Carmichael Nov. 28, 1899 871,580 Forrester Nov. 19, 1907 2,451,492 Johnson Oct. 19, 1948 

1. IN A HIGH TEMPERATURE FURNACE COMPRISING A HEATINSULATED STRUCTURE PROVIDING A PROCESSING CHAMBER ADAPTED TO CONTAIN A BATH OF MOLTEN LIQUID, THE COMBINATION THEREWITH COMPRISING TWO LIQUID CIRCULATING CHAMBERS WITHIN THE INSULATED STRUCTURE, A FIRST ONE OF SAID CIRCULATING CHAMBERS HAVING AN INTAKE PASSAGE COMMUNICATING WITH THE PROCESSING CHAMBER, SAID INTAKE PASSAGE BEING AT A LEVEL TO RECEIVE MOLTEN BATH LIQUID FROM SAID PROCESSING CHAMBER BY GRAVITY FLOW, THE SECOND ONE OF SAID CIRCULATING CHAMBERS HAVING AN OUTLET PASSAGE COMMUNICATING WITH SAID PROCESSING CHAMBER TO RETURN MOLTEN BATH LIQUID THERETO, SAID OUTLET PASSAGE BEING AT A HIGHER LEVEL THAN SAID INTAKE PASSAGE AND AT A LEVEL HIGH ENOUGH TO RETURN THE MOLTEN BATH LIQUID BY GRAVITY FLOW TO THE PROCESSING CHAMBER, A COMMUNICATING DUCT IN SAID INSULATED STRUCTURE BETWEEN THE TWO CHAMBERS FOR PASSAGE OF MOLTEN BATH LIQUID FROM THE FIRST CIRCULATING CHAMBER TO THE SECOND, THE DUCT COMMUNICATING WITH THE TWO CIRCULATING CHAMBERS ABOVE THE SAID INTAKE AND OUTLET PASSAGE THEREOF, MEANS IN SAID HEAT-INSULATED STRUCTURE TO CAUSE SAID MOLTEN BATH TO CIRCULATE BY GRAVITY FROM SAID SECOND CHAMBER, THROUGH THE PROCESSING CHAMBER, AND BACK TO SAID FIRST CHAMBER, SAID MEANS COMPRISING A PIVOTED ROCKER MEMBER PARTLY EXTENDING INTO SAID DUCT AND HAVING A SCOOP PORTION WHICH IN ONE POSITION OF THE ROCKER DIPS INTO THE LIQUID OF THE FIRST CHAMBER, THE ROCKER MEMBER PROVIDING A CONVEYING PORTION COMMUNICATING WITH THE SCOOP PORTION INTO WHICH THE LIQUID FLOWS FROM THE SCOOP PORTION WHEN THE LATTER IS RAISED, THE CONVEYING PORTION THEREUPON SUPPLYING THE LIQUID TO THE SECOND CHAMBER, AND MEANS FOR OSCILLATING THE ROCKER. 